The present invention relates to apparatus for controlling cuff pressure in an endotracheal tube.
Endotracheal tubes are well known. In use, an endotracheal tube is inserted through the mouth of a subject into the trachea for facilitating ventilating of the subject from a ventilator or other suitable ventilating medium source. Typically, an endotracheal tube terminates at one end in a coupling for coupling the tube to a supply tube which supplies the ventilating medium source. A inflatable cuff is provided at the other end of the endotracheal tube and extends around the tube so that on inflating of the cuff the endotracheal tube is secured in the trachea of the subject and leak passed of the ventilating medium into the mouth of the subject is avoided during the inrspiratory phase of each breathing cycle. A communicating tube is provided on the endotracheal tube for communicating with the cuff and for facilitating inflating of the cuff. Typically, the communicating tube extends along the side of the endotracheal tube, and ideally, forms an integral part therewith. Typically, the cuff is manually inflated by a syringe to a pressure which is adequate for retaining the endotracheal tube in the trachea and also for preventing leak passed of the ventilating medium. However, care is required in order to avoid over-inflating the cuff, which could lead to injury and trauma, and in particular, to damage of the vocal cords of the subject.
Due to pressure variation of the ventilating medium during a breathing cycle, for example, the pressure variation as a breathing cycle transitions between the inspiratory phase and the expiratory phase, and indeed, over a series of breathing cycles, it is difficult to achieve an adequate degree of sealing of the endotracheal tube between the cuff and the trachea for all such pressure variations to avoid leakage of the ventilating medium into the mouth of the subject.
Additionally, in order to facilitate manual inflating of the cuff by a syringe which can deliver a relatively large volume of air at a relatively low pressure, it is necessary in general to form the cuff from a relatively highly compliant material, for example, a latex material which will inflate at relatively low pressures. However, latex materials suffer from a number of disadvantages. Firstly, latex materials cause allergies in many people, secondly, latex materials tend to be permeable to some of the anaesthetic gases, such as nitrous oxide which can permeate into the cuff. Since the latex material is a highly compliant material, as the nitrous oxide permeates into the cuff the cuff further inflates, and this can cause trauma and indeed, serious injurious effects to the subject.
A further problem with known endotracheal tubes, and in particular, endotracheal tubes which are adapted for manually inflating with a syringe, or indeed, are adapted for inflating by a compressed air source is that a check valve is required in the communicating tube to the cuff for maintaining the cuff inflated after it has been disconnected from the syringe or compressed air source.
Attempts to overcome these problems associated with endotracheal tubes have been made. In particular, attempts have been made to provide apparatus for varying the cuff pressure as the pressure of the ventilating medium varies, in other words to provide high cuff pressure during the inspiratory phase of each breathing cycle and low cuff pressure during the expiratory phase. In general, such apparatus require that the cuff be inflated from an external source, typically an external compressed air source, such as a compressed air source available in a hospital. This, thus requires that the endotracheal tube as well as being connected to a ventilator must also be connected to a separate compressed air source, and in the absence of such a compressed air source the endotracheal tube must be connected to a large pressurised gas cylinder, or alternatively the endotracheal tube cannot be used. A valving system which generally includes solenoid operated valves and a pressure regulating system are also required for controlling and regulating the pressure of the air or gas from the external source for supply to the cuff. Such systems suffer from the disadvantage that they are slow to react, and in general are unable to accurately. track transitions between the inspiratory and expiratory phases of breathing cycles.
U.S. Pat. No. 4,825,862 of Sato discloses apparatus for regulating cuff pressure in an endotracheal tube. The apparatus comprises a pressure regulator for regulating the pressure of a separate gas supply to the cuff in response to pressure variation in breathing cycles. However, the regulator disclosed in this U.S. specification is a mechanically operated regulator, and in general, would be relatively slow to react, and in general, would be unable to react with the speed required to vary the pressure during individual breathing cycles. However, irrespective of whether the regulator of the apparatus of Sato would be capable of tracking the pressure variation of the ventilating medium during each breathing cycle, the apparatus of Sato requires a separate gas supply, in other words, the apparatus of Sato would have to be connected to an external gas supply, for example, a hospital compressed air system or other such external source.
U.S. Pat. No. 5,235,973 of Levin son also discloses a cuff pressure controller for controlling cuff pressure of an endotracheal tube in which the cuff pressure is held at a high pressure during the inspiratory phase of a breathing cycle, and is held at low pressure during the expiratory phase. However, the cuff pressure controller of Levinson requires the supply of gas from a separate external gas source for inflating the cuff of the endotracheal tube. Additionally, pressure control valves for controlling the pressure of the gas supply to the cuff are also required.
Accordingly, there is therefore a need for apparatus for controlling cuff pressure of an endotracheal tube for minimising leak past of ventilating medium into the mouth of the subject during the inspiratory phase of a breathing cycle, and which avoids the need for having a separate external pressurised gas source for inflating the cuff.
The present invention is directed towards providing such apparatus.
According to the invention there is provided apparatus for controlling cuff pressure in a cuff of an endotracheal tube, the apparatus comprising a control means for controlling the pressure of an inflating medium for inflating the cuff at respective first and second pressure levels during the inspiratory and expiratory phases, respectively of each breathing cycle of a subject, wherein the apparatus comprises an inflating medium supply means for supplying inflating medium to the cuff, and the control means controls the inflating medium supply means for supplying the inflating medium at the second pressure level to the cuff during the expiratory phase of each breathing cycle.
In one embodiment of the invention the inflating medium supply means is a variable pressure inflating medium supply means.
In another embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the first pressure level to the cuff during the inspiratory phase of each breathing cycle.
In another embodiment of the invention a monitoring means is provided for determining the transitions between the respective inspiratory and expiratory phases during a series of sequential breathing cycles, and the control means is responsive to the monitoring means for controlling the inflating medium supply means for supplying the inflating medium to the cuff at the respective first and second pressure levels during the inspiratory and expiratory phases, respectively, of each breathing cycle.
Preferably,the monitoring means monitors the pressure of the ventilating medium to the subject, and the control means is responsive to the monitoring means for controlling the inflating medium supply means for supplying the inflating medium at the first pressure level as a function of the pressure of the ventilating medium during the inspiratory phase of each breathing cycle.
Advantageously, the control means controls the inflating medium supply means for supplying the inflating medium at the first pressure level tracking the pressure of the ventilating medium during the inspiratory phase of each breathing cycle.
In one embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the first pressure level similar to the pressure of the ventilating medium during the inspiratory phase of each breathing cycle.
In another embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the first pressure level at a pressure differential relative to the pressure of the ventilating medium during the inspiratory phase of each breathing cycle.
In a further embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the first pressure level at a predetermined pressure above the pressure of the ventilating medium during the inspiratory phase of each breathing cycle. Preferably, the predetermined pressure by which the first pressure level of the inflating medium is above the pressure of the ventilating medium during the inspiratory phase of each breathing cycles lies in the range of 1 mBar to 10 mBar. Advantageously, the predetermined pressure by which the first pressure level of the inflating medium is above the pressure of the ventilating medium during the inspiratory phase of each breathing cycle lies in the range of 2 mBar to 3 mBar.
In another embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the first pressure level at a predetermined pressure below the pressure of the ventilating medium during the inspiratory phase of each breathing cycle. Preferably, the predetermined pressure by which the first pressure level of the inflating medium is below the pressure of the ventilating medium during the inspiratory phase of each breathing cycle lies in the range of 5 mBar to 20 mBar.
In an alternative embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the first pressure level at a constant predetermined first pressure level.
In one embodiment of the invention the monitoring means monitors the pressure of the ventilating medium in the endotracheal tube. Advantageously, the monitoring means comprises a pressure transducer, and preferably, the ventilating medium is teed off from the endotracheal tube to the monitoring means.
In one embodiment of the invention the medium for inflating the cuff at the first pressure level during the inspiratory phase of each breathing cycle is derived from the ventilating medium. Advantageously, the ventilating medium is derived from the endotracheal tube. Preferably, the control means comprises a valving means for supplying medium to the cuff for inflating thereof, the medium being derived from the ventilating medium and the inflating medium supply means during the inspiratory phase of each breathing cycle, and from the inflating medium supply means during the expiratory phase of each breathing cycle. Advantageously, the valving means comprises a means for valving the medium of highest pressure of the inflating medium and the ventilating medium to the cuff. Ideally, the valving means comprises a pair of one way valves connected respectively to the inflating medium supply means and to the endotracheal tube for supplying the inflating medium from the inflating medium supply means and the ventilating medium from the endotracheal tube to the cuff.
In one embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the second pressure level at a second predetermined pressure level.
In another embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the second pressure level at a predetermined pressure below the pressure of the ventilating medium during the inspiratory phase of each breathing cycle.
In a further embodiment of the invention the control means controls the inflating medium supply means for supplying the inflating medium at the second pressure level at a predetermined constant pressure.
Preferably, the second pressure level is less than the first pressure level.
In one embodiment of the invention the inflating medium supply means comprises an inflating medium supply pump. Preferably, the inflating medium supply pump is provided by an electric motor operated pump. Advantageously, the electric motor of the inflating medium supply pump is controlled by the control means.
Preferably, a smoothing means is provided for smoothing the pressure of the inflating medium from the inflating medium supply means. Advantageously, the smoothing means comprises a reservoir defining a buffering chamber for buffering the inflating medium.
In one embodiment of the invention a pressure reducing means is provided for reducing the pressure in the cuff as each breathing cycle is transitioning from the inspiratory to the expiratory phase. Preferably, the pressure reducing means comprises an exhaust vent from the smoothing means, the exhaust vent being of relatively small bore size such as not to significantly affect the pressure of the inflating medium at which the inflating medium is being supplied to the cuff.
In one embodiment of the invention an input means is provided for facilitating inputting of a command to the control means relating to the first and second pressure levels. Advantageously, the input means comprises an input keypad.
Preferably, the control means comprises a microcontroller.
In a preferred embodiment of the invention the apparatus comprises a housing, and the inflating medium supply means and the control means are located within the housing. Preferably, the monitoring means is located within the housing. Advantageously, the smoothing means is located within the housing. Preferably, the input means is located in the housing and is externally accessible. Ideally, toe housing is adapted for pole mounting on or beside a bed of a subject
In an alternative embodiment of the invention the apparatus is adapted for mounting in a ventilator supplying the ventilating medium, and preferably, the apparatus is responsive to the ventilator transitioning between the respective inspiratory and expiratory phases of the breathing cycle.
In a further embodiment of the invention the apparatus also comprises an endotracheal tube. Ideally, a bleed off means is provided from the endotracheal tube for bleeding off ventilating medium from the endotracheal tube to the valving means and/or the monitoring means.
In one embodiment of the invention a communicating means is provided from the endotracheal tube for communicating with the inflating medium supply means.
In a further embodiment of the invention the endotracheal tube terminates at the end opposite the cliff in a coupling for coupling the endotracheal tube to a ventilating medium supply source.
In a still further embodiment of the invention the endotracheal tube comprises an adapter for facilitating connection of the delivery means and the connecting means to the endotracheal tube.
The advantages of the invention are many. Two important advantages of the invention are firstly, that the apparatus allows the pressure to which the cuff is inflated to track in real time the pressure of the ventilating medium, and secondly, the apparatus provides for a reduction in the pressure to which the cuff is inflated during the expiratory phase of each breathing cycle, thereby reducing discomfort to the subject, and also avoiding damage to the trachea and its related organs. Furthermore, use of the apparatus according to the invention allows an endotracheal tube to be used without the need for an additional external source of pressurised gas for inflating the cuff of an endotracheal tube. The provision of the inflating medium supply means in the apparatus according to the invention supplies the inflating medium directly to the cuff. Additionally, by providing the inflating medium supply means in the apparatus a relatively simple apparatus is provided, and the inflating medium can be supplied to the cuff without the need for complex solenoid operated valving systems, and without the need for a complex pressure regulating valving system. Additionally, by virtue of the fact that the inflating medium is directly supplied by the inflating medium supply means in response to the monitored pressure of the ventilating medium the apparatus responds relatively quickly to the transition between the inspiratory and expiratory phases of each breathing cycle, and between the expiratory and inspiratory phases of sequential breathing cycles. The provision of the inflating medium supply means as an electrically powered pump provides a particularly efficient and quick to respond apparatus, and providing the control means as a microcontroller further enhances the response time of the apparatus for supplying the inflating medium at the respective first and second pressure levels in response to transitions between the inspiratory and expiratory phases of each breathing cycle.
Furthermore, by virtue of the fact that the cuff is continuously inflated, the need for a check valve for preventing deflation of the cuff is no longer required. By virtue of the fact that the cuff is continuously inflated there is no need for the cuff to be provided by a highly compliant material such as a latex material, the cuff may be provided by any suitable inflatable material, and typically, would be of a plastics material. This, thus, allows the endotracheal tube to be provided without the need for a latex material thus avoiding any danger of allergic reactions in a subject. Furthermore, since the cuff is continuously inflated the leaking of anaesthetic gases into the cuff has no effect on the inflating of the cuff, and furthermore, even if the cuff is of a material which is permeable to any of the anaesthetic gases, or indeed any other media being supplied to the subject there is no danger of over-inflating of the cuff. Additionally, the fact that the cuff may be provided in a less compliant material also reduces any danger of over-inflating of the cuff.
A further advantage of the invention is that it provides a relatively simple control apparatus for controlling cuff pressure at two levels, thereby allowing the cuff pressure to be relaxed to the lower second pressure level during the expiratory phase of the breathing cycle and raised to the higher first pressure level for minimising leakage of the ventilating medium into the mouth of the subject during the inspiratory phase of the breathing cycle.